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How does altimeter reading vary when departing from ISA conditions?
I am a soon-to-be student-pilot and am struggling with a basic concept that is altitude. After watching multitude of online videos, I feel that most of the people do not have good teaching skills.
Introduction
The altimeter is a barometer, it reads atmospheric pressure. At 0' altitude, it should measure "this certain pressure that we find at 0'" and indicate 0'. This is obtained by setting the reference pressure in the Kollsman window measured somewhere near the airport. One day it might be 1013 hPa, others it will be 998 hPa or 1036 hPa.
The Scenarios
We are in the aeroplane, at the airport which is at MSL (0' altitude).

SCENARIO 1 (International Standard Atmosphere):

Elevation: 0', temperature: 15 C, pressure: 1013.25 hPa
METAR reads QNH 1013

we set our Kollsman window to 1013 => it correctly indicates 0' altitude
we set it to less than 1013 => it will indicate more than 0' (say 230') LESS than 0'!
we set it to more than 1013 => it will indicate less than 0' (impossible but bear with me) MORE than 0'

SCENARIO 2 (low pressure):

Elevation: 0', temperature: 15 C, pressure: 998 hPa
METAR reads  QNH 998

set our Kollsman window to 998 => it correctly indicates 0' altitude
set it to less than 998 => it will indicate more than 0' (say 230')
set it to more than 998 => it will indicate less than 0'

If I got the above correctly than the following should apply too:
SCENARIO 3 (International Standard Atmosphere):

Elevation: 5000', temperature: 5 C (as per lapse rate, -2C for every 1000'), pressure: 847 hPa (as per lapse rate, -1hPa every 30')
METAR reads  QNH 1013 (actually our pressure of 847 hPa, adjusted down to MSL)

set our Kollsman window to 1013 => it correctly indicates 5000' altitude
set it to less than 1013 => it will indicate more than 5000' (say 6200')
set it to more than 1013 => it will indicate less than 5000'

My Questions
What happens at this altitude of 5000' if we move out of the ISA?

if the temperature drops further to, say -2 C?
if the pressure goes up to 900 hPa?

EDIT (answer):
My premise of "...we set it to less than 1013 => it will indicate more than 0' (say 230')" was wrong all the time! By setting the pressure in the Kollsman window we are effectively "telling" the altimeter at which pressure the 0' elevation is (or what is the pressure at 0' elevation).
If we "tell it" that the 0' is at 1000 hPa, and it is still sensing 1013 hPa as I initially stated, it will indicate only possible altitude - LESS than 0', not more.

Where is the question?

@EugeneStyer Last three lines.

Eugene Styer - Well, the question is basically - is this all correct? :) If it is, then, there are two sub-questions at the very end of my post. If not, then it's back to the drawing board for me. Thanks!

Forgive me but TLDR.  Could you please edit to make it digestible?  As it is, I have no idea what your doubt is.

Simon - the doubt is: how do I set my altimeter? There is more than one scenario as there are two variables, which can vary in two directions. You don't have to read it all, just go through the bold points.

If you're just setting it, then it's QNH or QFE as directed by ATC, if controlled, or according to jurisdiction which you haven't specified.  Sorry, it's probably me being dense but I still don't get what you're asking.

Simon i appreciate your effort but unless you take the time and read all of my scribbling we won't get anywhere :). I apologize if this is too long but I come from StackOverflow where such questions and explanations are more than welcome. Cheers!

Are you looking for what the altimeter display will indicate with those change in conditions? A pressure altitude instrument will follow the ISA, unless it is using an OAT probe and actually providing you with the density altitude.

Please note that along with changing conditions I am also making adjustments in my Kollsman window (that is the 3 bulletpoints in each of my Scenarios). Thanks.

Remember the saying,  "From high to low, look out below."  Works for both pressure and temperature.  That should answer all your questions.  For more information look up cold weather altimeter corrections.

What happens at this altitude of 5000' if we move out of the ISA?
if the temperature drops further to, say -2 C?
if the pressure goes up to 900 hPa?

If we summarize this as saying simply, what happens if the pressure changes en route (as I think that is what you are asking). The answer is simply, change your altimeter setting! As a matter of fact generally when flying if you are getting flight following or talking to a controller in any kind they will give you the local altimeter setting when you approach the area. Your read back of this setting is required and important for this very reason.  If you are not on with control, you should be picking up local weather from airports along your route to ensure a proper local altimeter setting.
You are correct that all altimeters are calibrated for ISA and variance in these conditions will lead to an incorrect reading. In some cases you may need to apply a correction. You can find a comprehensive guide on how to do so here.

When To Apply Corrections
When the aerodrome temperature is 0°C or colder, the temperature error
  correction must be added to:

DH/DA or MDH/MDA and step-down fixes
  inside the final approach fix (FAF).
All low altitude approach
  procedure altitudes in mountainous regions (terrain of 3000 ft AMSL or
  higher)

If you are at an airport you should set the altimeter to the current field altimeter setting as per the ATIS. The ATIS generally is updated frequently or if a condition change warrants it. In some cases at a towered field the tower may update you in real time if the current altimeter varies from the ATIS. If none of these tools are present to you, and there is no local weather to draw from you should set your altimeter to the known local field elevation (as per your chart or AF/D) prior to departure. This should be done before every flight. If the conditions change, so should your altimeter setting.

Dave, thanks for the comment but actually this is a "step after" my question. I am still not flying from area to area, but rather waiting at an airport, trying to set my instrument correctly. :)


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Center of Gravity and Center of Lift stability
I have recently been reading about the center of gravity and center of lift. On the German Wikipedia there are many different graphics about the relation between the center of gravity and the center of lift. The one that struck me the most is the one where the description is the one where the center of gravity is the same as the center of lift:

Image according to: https://en.wikipedia.org/wiki/Wikipedia:Image_use_policy
The article in Wikipedia mentions that having a center of gravity (theoretically) coincide with the center of lift constitutes for a very unstable aircraft. It says that even the slightest turbulence will cause very bad nose attitude changes as the airplane becomes very unstable along the lateral axis.
I am having a really hard time understanding how this is any different from any other CG/CL configuration. Why is the airplane more laterally stable if the center of gravity is in front of the center of lift and the elevator is compensating the ensuing torque around the center between center of lift and gravity?

I'm wondering if you meant to say the longitudinal axis rather than the lateral axis. Fore and aft are measured along the longitudinal axis. If a sudden gust increases the angle of attack momentarily, a center of lift aft of the c.g. will counter the momentary increase in lift with a nose down force to provide stability by reducing the angle of attack. The rudder is not involved in this resolution of forces.

I think the confusion here is because in longitudinal stability we look at rotations (pitch) about the lateral axis (y-axis in the body reference system). So probably the wikipedia article talks about longitudinal stability when it mentions "unstable along the lateral axis"

@DeltaLima It would be more clever to talk about the pitch axis. Never mind that this article seems to perpetuate a myth that is untrue.

@DeltaLima The Wiki article was even worse, it talked about the "horizontal axis" as if the airplane only has one horizontal axis. I inferred they mean pitch around the lateral axis (i.e. the lateral axis is the axis of rotation).

@Terry you're back! Nice to see you!!

If you ever read something along the line that "even the slightest" cause will result in "very bad changes" when before all was stable, you know that the writer was out of their depth. But you have come to the right place.
The way you formulate the question it concerns lateral stability. The combined center of all side forces (= lateral lift) should be behind the combined center of gravity of all components of the airplane to give it weathervane stability. Since the law of conservation of momentum applies also to a flying airplane, all movements should happen around its center of gravity, so all moments should be summed up there to see what effect they will have. In order to see their effect on stability, it is even better to focus on the force changes effected by a change in sideslip. If they produce a moment which will rotate the airplane away from that sideslip, the airplane is laterally stable.
Why only the changes in sideforce with sideslip? This will become more clear when we look at longitudinal stability, which is implied by the graphic in your question. Here the same principles apply, only that a constant downward acceleration is added, namely gravity. To compensate its weight, the airplane needs to produce an opposite force, namely lift. This lift has to act at the same longitudinal and lateral position of the center of gravity. Any deviation would produce a moment around that center of gravity which would start a rotation. In order to shift the center of lift to the desired location, the pilot will deflect control surfaces to modulate the lift force at the extreme ends of the airplane (tail rsp. canard and wingtips) so that any moment around the center of gravity disappears. This is one meaning of "trimming" the airplane (the other one means to remove all stick forces in order to stay at this state).
Theoretically, the pilot could balance the airplane in the desired state using the control surfaces like you can balance a broom on your fingertip. But that becomes tiring quickly. So it is preferable that the airplane itself will produce moments when the trimmed position is left, without any additional control deflections. This is achieved by having the changes in lift force act at a location behind the center of gravity.
The point where all lift forces can be summed up is the center of pressure, (Auftriebsmittelpunkt) whereas the point where all changes can be summed up is the neutral point (Neutralpunkt). Now you know what the author of the Wikipedia article wanted to say but failed to do so. He is by far not the only person to confuse those two points.
In fact, only when the center of lift coincides with the center of gravity will flight be straight and steady. All other positions will cause the airplane to rotate away from its current attitude. In order to return to its old state, only the neutral point needs to behind the center of gravity.

I actually think wikipedia was about longitudinal stability, but since that looks at pitching moments which are around the lateral (y-)axis, the OP got confused.

@DeltaLima I wasn't sure so I covered both. I tried to find the article but was unsuccessful.

I think some of the confusion is over the precise definition of  "Center of Lift", where it's generally thought of as applying only to the wing (a fulcrum point representing the forces holding the airplane up so to speak), but in your definition it's the "whole body" center of lift which takes into account the addition or subtraction of other lifting components being used for trim. The pitching force balance that constitutes trim, the "target AOA" that the static stability forces will orient toward, occurs with the whole-body C of L is coincident with the C of G.  Is that about right?

@JohnK The whole body definition of center of lift is much more useful that that of only the wing, but harder to calculate. That is precisely because as you are rightly saying, when both, the CoL and the CoG, match length- and sidewise the airplane is trimmed.

My terms might be a bit confusing, I figured the tendency to (or not to) rotate around the lateral axis could be considered the lateral stability :). I.e. how much the nose of the aircraft moves up or down.

@PeterKämpf isn't the point where all changes of lift can be summed up an aerodynamic centre, and a neutral point is a CG location in which neutral stablity is achieved?

A quick refresher:  the lateral axis runs through the wings and rotates in pitch.  The vertical axis runs through the top to bottom and rotates in yaw. The longitudinal axis runs nose to tail and rotates in roll.
So we talk about longitudinal stability around the lateral axis. (Ah ha!) So the relevant control surface is the elevator.
Placing the center of wing lift near the center of gravity is not necessarily a horrible thing if there is adequate surface area behind the center of gravity (for both vertical and horizontal stabilizers) for the aircraft to be directionally stable.
Placing the center of gravity ahead of the center of wing lift allows us to use tail downforce to trim for constant airspeed.  The is called static stability.
However, fuel conscious long distance cruisers such as airliners (and gliders) can save a little bit of drag (drag = thrust = fuel = $) by "relaxing" static stability tail downforce, allowing the wing to most efficiently do all the lifting work.
Pilots flying these aircraft must beware of unwanted airspeed changes, where as staticly stable aircraft can be "trimmed" for a specific airspeed.
Edit for Yanick Salzmann:
Regarding the final paragraph concerning lateral stability (about the vertical axis), which would use the rudder as the control surface, setting the CG forward by default increases lateral stability.  Interestingly, control surfaces such as the elevator and rudder introduce instability when applied.
The rudder applies torque to the center of gravity in order to change the direction of flight.  It must overcome stabilizing forces to do this.
Making the plane more stable makes it harder to turn, which is why too much is not good.

I really like this analogy. Turning the airplane upside down and imagining it like a table makes it very obvious why its more stable!

Regarding your edit, I probably made it more confusing, I think it might be easier to go down to very simple terms: Making the nose of the airplane go up or down. Thats what I understood from the Wikipedia article (it is very poorly worded).

Ah, I realized I mistakenly mentioned the 'rudder' in my question, I meant the elevator.

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Standard Size to Print a sectional chart?
What sizes does the sectional charts are sold at?
I downloaded it from here, and was able to print it on a large format printer.
https://www.faa.gov/air_traffic/flight_info/aeronav/productcatalog/vfrcharts/Sectional/
As it is a TIFF image, based on the image resolution it ended up to be approximately 42" X 60". Which I believe is accurate as when one prints this way, based on the resolution, and the amount of pixels, it calculates the size by itself.
Which is good, however, I am looking for a standard size that the charts you buy come with, so I can verify what I printed. Also, give inputs to my printer, to print that paper size. If any of you have purchased a sectional chart, can you give me the size of it? Or even provide an image of the same.
I checked this Stackexchange link here:
What's the standard print size for a sectional chart?
The answer over there is -  20 3/4" X 59 1/4". However that does not seem to be matching the size (aspect ratio) of TIFF images on the FAA website. It is exactly half of what it supposed to be. So any suggestions would be appreciated. Unless otherwise it is being folded.

The 1:500,000 scale is important if you want to use any of the standard tools with the sectional chart.

I agree with Erin Anne, sectional charts are more or less compliant with ICAO 1:500,000.

I believe the issue with the aspect ratio is because the sectional is printed 2-sided with the north half on one side and the south half on the other. The TIFF file combines them.

It is exactly half of what it supposed to be.

Sectionals are printed on both sides.  The electronic copy contains the information that is on the front and back.

Thanks that answers the question and confusion

Unfortunately, there are only two ways of printing a sectional for your uses with a standard plotter.

Find a wide-format printer to print out the chart at the proper size.
Print out only a part or a section of the sectional chart at the proper resolution.
Buy an actual sectional chart. They are probably the cheapest things for which you will ever pay in aviation. Even if you laminate them (Marcels sells cheap self-service lamination and Vis-a-Vis markers). Some aviation/pilot shops will charge half price and even less for expiring or expired charts.

I think the issue that you are having is that you are confusing resolution, size, and scale.

Resolution roughly means detail and clarity when printed at the proper size. It is truly the number of pixels per unit of area based on the source material.
Size means the 2-dimensional area of the paper on which it was intended to be printed.
Scale simply means the ratio of the size of the printed object compared to the actual object.

They are all separate measurements.
The FAA website says “The files are 300 dots per inch and 8-bit color.” This only applies when printed on paper that is 20 3/4" X 59 1/4". Printing on smaller paper, theoretically, should give you greater resolution (which is not really the case). Even though it makes it harder to distinguish detail. Printing on larger paper will give you poorer resolution to the point that the image will be pixelated. Even though it may make it easier to distinguish detail up until pixelation of the images.
Think of it like watching Standard Definition programs on an 80” diagonal television. You will have the size. But not the resolution. The same is true for the opposite.
One option to try with a regular printer is to print the sectional at the proper resolution and size. Your printer probably uses regular 8.5x11” letter paper. It may have an option to use the original scale of the image and not scale to size. It may also have the option of how you want the image divided on the size of paper available. If you have a way of previewing the printed image as it would appear on paper (many printer programs do), you can choose which page(s) you wish to print.
As an aside, the sectionals used on the FAA (“written”) Knowledge Exams are also not to scale. You will have to measure your distances using the scale in the chart legend.

This is all good info. I figured my question could use more detail, so I edited the question.

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What is the content of a Letter of Agreement between the Collaborative Decision Making participants?

Can you give a sample of a Letter of Agreement?
How to calculate average taxi time at airport?

Something like this: http://cdm.fly.faa.gov/wp-content/list_yo_files_user_folders/cdm_editor/cdm_doc/CDM%20MOA.docx ??

These appear to be two completely separate and only slightly related questions.  Should this be split into two different questions?

First, a little bit about CDM and the participants that make up the team.  The FAA's CDM Website provides the following overview:

Collaborative Decision Making (CDM) is a joint government/industry initiative aimed at improving air traffic flow management through increased information exchange among aviation community stakeholders. CDM is comprised of representatives from government, general aviation, airlines, private industry and academia who work together to create technological and procedural solutions to the Air Traffic Flow Management (ATFM) challenges faced by the National Airspace System (NAS).

This "team" of government/industry representatives is called the CDM Stakeholder's Group (CSG). There is a "Membership Agreement" that all parties of the CSG sign. This agreement outlines the roles and responsibilities of the FAA and each CSG member. It provides "rules" and processes for exchanging data and resolving disputes should any arise. It outlines the methods by which to modify the agreement, and how long the agreement should last.
A sample of the agreement letter that the FAA provides to each stakeholder member of the CSG is available to view here: http://cdm.fly.faa.gov/wp-content/list_yo_files_user_folders/cdm_editor/cdm_doc/CDM%20MOA.docx

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Effect of heat and humidity on take off, descent, climb, and cruise
I am aware of this question, this resource (phak), and this resource that explains the science, but I am looking for a more straightforward answer.
I am student pilot and there's a lot of literature on "if there is more heat and humidity, then I need a longer takeoff and reduced rate of climb" and many variations of this statement (e.g. cold and high elevation, etc). But it's all sort of a bit confusing to me.
In the resource I linked above, it says that high temperatures mean the air is less dense but high humidity can add to the pressure so overall the density pressure is increased I need a longer takeoff. But why wouldn't the higher temperatures and humidity not cancel each other out?
I was wondering if someone could perhaps break it down as follows:

Hot temperatures, high/low humidity, sea level
Hot temperatures, high/low humidity, high elevation
Cold temperatures, high/low humidity, sea level
Cold temperatures, high/low humidity, high elevation

For the 8 above conditions, what is the general effect in aviation for take-off, landing, and rate of climb?

You used the phrase "density pressure" in your question. You are talking about "density altitude" in that sentence. Density and pressure are two separate properties of air.

If you”re looking for an explanation of the cause of change in TO distance:

Air expands when heated, so a warm kilo of air needs more cubic meters than a cold kilo. If it cannot expand like in a closed conrainer, the pressure will increase. If it can expand, there will be fewer air molecules.
Water molecules weigh less than air molecules. If some water molecules are replacing air molecules at ambient pressure, a cubic metre of humid air will be lighter that a dry m$^3$ and the reduced density will result in less lift.$^1$
The atmosphere thins out at higher altitudes. There are fewer air molecule to support the aircraft weight.

With the above in mind, realising that air density is a defining factor in creating power and lift, it should be easy to cross oit the four listed items in the question :)
Update This answer contains a graph on how humidity and temperature reduce air density.
—————-
$^1$ The effect on density is actually very small, main issue is the reduction in power, most noticable in piston engines. But as a mnemonic it should work.

High temperature reduces engine power due to lower air density (the engine thinks it's at higher elevation), and high humidity reduces engine power because the humidity slows the burn rate of the charge in the engine's cylinder, which has a power reduction effect similar to retarding spark timing; peak cylinder pressure is reached too late to get the most out of the pressure rise in applying leverage to the crankshaft.
How the order your list will depend on the magnitude of each parameter relative to the others, so there are too many variables.
The bottom line is simple:
Lower, colder, drier = better.
Higher, hotter, humid-er = worse.

Maybe this is somewhat counter intuitive to me but if the temperature is higher, why would the plane think it's at a higher elevation. Does temperature typically drop as we go  up in elevation?

@Jonathan The plane does not care about elevation, it cares about air density, and warmer air is less dense similarly to air at higher altitude.

@John K Why colder air is better? Doesn't it reduces thermal efficiency of engine? Or because it has higher density than hotter one?

No the colder the air charge the better.  The power is coming from the absolute temperature rise from combustion and you don't get a boost from the initial charge being hotter, but you DO get a boost from the charge being denser. At the extremes, like with turbocharged engines, the air charge, although dense from being compressed, is so hot that it eats into detonation margins and you have to either retard the ignition timing or use an intercooler to lower the air charge temperature.

"humid-er" -> "wetter", but, TBH, I like "humid-er". ;)

I was concerned people would confuse humider with humidor, one of those cigar cabinets lol

@JohnK If higher LDA is bad, how come commercial jets typically fly in such high elevations? I understand that there is less drag, traffic, and turbulent weather at that elevation, giving better fuel efficiency. But are the cons of lower air density offset by the pros of better fuel efficiency?

“High” and “low” for each of those factors is relative, and I can’t explain how they combine together without resorting to math. Luckily, it suffices to learn which direction each of those factors (in isolation) will move the Density Altitude.
Density Altitude is a single number that tells you how well your plane will perform (how much power your engine will produce and how much lift your wings will produce) under a particular set of conditions. That, in turn, dictates runway required and climb rate.
Low DA is good. High DA is bad.
You are not expected to remember how to calculate the exact DA; there are apps for that, and some AWOS will even tell you directly. But you’re expected to know what conditions will lead to a high DA, and why that can be so dangerous, so that you recognize when there’s a potential hazard to be mitigated.

If higher LDA is bad, how come commercial jets typically fly in such high elevations? I understand that there is less drag, traffic, and turbulent weather at that elevation, giving better fuel efficiency. But are the cons of lower air density offset by the pros of better fuel efficiency?

@Jonathan It is mostly a problem for normally aspirated piston engines, which lose power with altitude. Turbine aircraft don’t, which is why they can fly much higher generally; they just need longer runways. But even airliners can have problems at high and hot airports like PHX and LAS.

Ahh i see. I suspected that but wanted to confirm. Thank you


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Untowered communication when abeam the airport
Let's say I have the following diagram

So, there's runway 28, and people take off straight out to the west towards the ocean. The runway is untowered and its right traffic for runway 28.
When I'm at point A denoted by the star, I can call out "something traffic, white archer 123 alpha over the coast inbound from the south for runway 28  something traffic"
I need to fly abeam the runway continue north and then swing in to join the downwind at a 45 degree angle for right traffic pattern for runway 28. So ideally I want to make a call at point B just to let people know where I'm at especially if there's someone taking off. What would be the right phrasing to report when I'm at position B?
I thought of the following but it seems to add more confusion.
"something traffic white archer 123 alpha over the coast abeam runway inbound for runway 28 something traffic."
The problem with this phrasing is, I don't want someone in the pattern getting confused that I'm going to come inbound by just making a right turn instead of swinging north.
Is there a better phrasing to let them know that I'm going swing around to the north and then join the right pattern?
UPDATE Nate Vaughan's post below makes a lot of sense and is instructional. The reason why I asked this question is because part of my training is to go to KOKB to practice untowered communications. That airport has the following traffic pattern:

As listed on their official website: http://www.oceansidemunicipalairport.com/resources.html
Hence, what would I do in this scenario when I'm at position B in my diagram?

Not a pilot myself but I would prefer "off the departure end of runway 28" rather than "abeam the airport", especially if you're trying to give a heads up to traffic that might be departing 28 (or even landing 10).

Holy cow, this is about the only situation Ive ever seen where our crazy UK "overhead join" actually simplifies things :D

If you are flying the noise abatement traffic pattern I would just announce:
"Oceanview Traffic Skyhawk NXXX flying off shoreline at traffic pattern altitude towards Santa Margarita River for right pattern downwind entry runway 24 Oceanview Traffic"
I don't think you need to specifically announce when you are abeam the runway especially when that far out.  The local traffic should know to avoid the offshore traffic.
However if you ever have questions about local airport procedures it is usually best to ask either the FBO or airport manager than an online forum.  Don't be afraid to call someone at the airport if you are not sure what to do.

If you are off shore at pattern altitude, you just entered at crosswind and can just fly the pattern rather than overshoot and do another entry, no? Shouldn't you still be above pattern altitude at this point?

Simple: don't fly at position B. Seriously, off the departure end of an untowered airport is the wrong place to be. Don't be there.
Instead fly over midfield at least 500' above pattern altitude, report when above midfield, and make a left 270 teardrop descent to the 45 degree arrow your diagram indicates. See Airplane Flying Handbook, 7-4.

I can’t upvote this enough…

Thank you, this is helpful. When I report I'm over midfield, how do I state my intentions of doing a left 270 teardrop descent? Can I make it literal like: "... over midfield doing left 270 to join right downwind runway 28 ..."

Hi Nate, please see update to my post. @MichaelHall

KOKB has special noise abatement procedures which prevent one from overflying the field.  The OP does not do a good job of explaining that.  Nose Abatement procedures request the pilot fly offshore and enter the downwind as shown in the OP's diagram.

Sorry for the ad hoc drawing, but the FAA‘s recommended procedure for entering the pattern in this case is as follows:

Pilot flies toward airport center at 500’ above TPA,avoiding either the approach or departure corridors for the runway.  Pilot would make radio contact on CTAF starting at a minimum of 10 miles from airport announcing intentions.

Passing midfield over the airport, still at 500 feet above TPA, pilot will announce position on CTAF and state intention to make a left teardrop for the 45° entry into the right downwind for runway 28.  Pilot will begin to descend while flying perpendicular to the runway outbound once clear of the traffic pattern.

once at traffic pattern altitude, pilot will begin a left turn to enter on a 45° line for the right downwind runway 28.

This isn’t exactly rocket science, but what you’re seeing out at that airport is a symptom of poor flight instruction for private pilots. Most instructors never teach students this and it could be an awful shock on a check ride when an examiner expects to see this.
As the previous poster said, it yes it is always wise to avoid the departure corridors of an airport especially untowered airports.


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Can we fly in Japan and/or Australia with EASA approved training and licences?
Disclaimer: I'm not a pilot, and seem to be lost with all the jargon and complexities around this matter despite trying to do adequate amount of research.

I am considering taking on my PPL in Hungary and it is all EASA approved training. Thereby the licence will be up to a standard of EASAs approval. Therefore with this licence, would I be able to fly in a foreign country such as Japan, Australia, etc. or other countries with whom EASA has a working arrangement?
If not how would I be able to switch over my PPL to be accepted in Japan and Australia?

Generally speaking, you need to hold a licence issued by the same country that the aircraft is registered in. There may be exceptions but you cannot fly an Australian aircraft on your EASA licence.
Luckily, converting a PPL between countries is generally straightforward when it has been issued by an ICAO-contracted state (which is most advanced countries and EASA).
For Australia, no additional tests are required (for PPL only, exams and flight tests are required for higher levels). You just need a medical, to pass a security check, and pay a fee. I believe EASA licences come with English Language Proficiency (ELP) level 4 to 6 so an English test is not required. Side note, the US does not have the ICAO ELP scheme so even native English speakers from there need to pass an English test when they convert to Australia.
I'm less familiar with Japan but according to AOPA Japan you need to sit a law exam and obtain a radio operator certificate.

Surely the US has only native speakers of American.

@Ben would this also include NFVR &/or IR?  provided I just have a PPL?

@3kstc Neither NVFR nor IR come automatically with a PPL. If you have them issued by EASA then they can be converted, but they require a flight test. If EASA hasn't issued them to you, you need to complete the training for each rating from the beginning. I don't know if Japan is different on that.


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Difference between "pressure levels raising on warm days causing lower IA" and "TA being higher than IA on warm days"
IA: Indicated altitude
TA: True altitude
I have seen this picture before:

Concept 1
and I understand this. On cold days, the pressure gradient is shorter which means the indicated altitude at a particular pressure setting will be lower. And on a warm day, the pressure gradient is steeper i.e. there are larger steps between pressure levels. Thus, the plane will indicate an altitude higher than true altitude. We know that altimeters measure pressure rather than density altitude.

Concept 2
But, we also know that pressure levels are raised on warm days and the indicated altitude is lower than true altitude. This also makes sense. On a warm day, temperature is higher cause a column of air to expand. Thus, at a particular true altitude there'll be more air above me than below me. This will exert more pressure on the top of the plane causing IA to be lower than TA.

But these two concepts seem to be contradicting. How do I reconcile these two bits of information??

Concept 3
If I'm flying from a region of cold air to warm air and if I'm keeping a constant indicated altitude, the plane will actually climb. This concept assumes that concept 2 is correct because once its in the warm air region the indicated altitude is lower than true altitude. And we've all heard the phrase "hot to cold, high to low, look out below." So this is all congruent. But if I chose to accept concept #1, then when I fly to a warmer region, my indicated altitude would be higher than true altitude and the phrase would be cold to hot, look out below.

Essentially, if I'm going to be flying on a particular day and the temperature is going to be significantly hotter than normal then am I going to plan with the notion :
A. that air density is lower which means the plane is going to think it's higher than it actually is?
B. Or pressure levels have raised causing the plane to think it's lower than it actually is?
mnemonic: I was told that when asked the question what will the IA be, I can ask myself what would I think. For example, if I'm at sea level and the temperature suddenly dropped would I think I'm up in the mountains? Likewise, if I'm at sea level and the pressure level suddenly dropped making it harder to breathe would I think I'm up in the mountains.
By this metric, I'd think that on a warm day, I'm NOT up in the mountains and hence I'd assume option B.
EDIT: I was actually the one who also asked this why are pressure levels raised on warm days but this question is a slightly different question and is not a duplicate.

Does this answer your question? Why are pressure levels raised on warm days?

@757toga Oops, I meant just altitude but accidently typed in IAS/TAS. I fixed the post.

@xxavier --the abbreviations are supposed to mean "Indicated Altitude" and "True Altitude"-- maybe the question should be edited to clarify this.

Concept 1:

On cold days, the pressure gradient is shorter which means the
indicated altitude at a particular pressure setting will be lower.

This is wrong, as you can see from the illustration--
The airplane in the blue (cold) airmass is only at about 7500', but is indicating 10,000'.  The indicated altitude is too high, not too low.
Concept 1 would be more correctly stated as "On colder-than-standard days, when the air column is more compressed, the isobaric surfaces1 are closer together, so the pressure gradient (i.e. change in pressure per unit change in altitude) is larger, which means that when the Kollsman window is set correctly for the pressure at the surface, the indicated altitude at any particular actual altitude is higher than it would be on a standard day.  Because there's more air below the aircraft, and therefore less air above the aircraft.  And the altimeter is really a pressure sensor, and the actual atmospheric pressure at any given point is based on the weight of the air column above that point.  So under these conditions, the aircraft is flying lower than the pilot would believe based on the altimeter.  The higher the AGL altitude2, the more pronounced this effect-- this effect vanishes at the surface, because there, all the air is above the aircraft, no matter how expanded or compressed the air column is."
Concept 2 is basically correct, and is just another variation of concept 1 as I've re-stated it above.
PS It's clear, from content posted in comments, that the original questioner is simply mis-reading the figure.  The vertical axis of the graph shows the true altitude, which is different for each of the three cases, and smallest for the cold case. Indicated altitude is the same for all three cases.
See answers to related ASE question Why are pressure levels raised on warm days?
Footnotes:

An isobaric surface is a surface of constant pressure.  A "pressure level" is basically the same thing, except that when we are talking about "pressure levels" we may be taking a 2-dimensional slice through the atmosphere, while an "isobaric surface" can be mapped out in three dimensions.

Or more precisely, the higher the aircraft is above the level of the station for which the Kollsman setting would be valid.

AHHH!  hahah I meant altitude again!!! My fingers are automatically typing airspeed, sorry about the recurring confusion. I fully meant altitude... my fault. Fixed.

In your answer, you state "On colder-than-standard days, ... the indicated altitude at any particular actual altitude is higher than it would be on a standard day." But this seems to conflict with the image I pasted, doesn't it? Or am I misunderstanding? Because, the picture suggests that the indicated altitude will be lower than TA on a colder than standard day.

I finally understood what you're talking about. My fault fully. I looked up a different version of that image: http://teterborousersgroup.org/wp-content/uploads/2015/09/TUG-How-High-are-you-Really-for_TUG.pdf and it made much more sense... You were right, I was completely misreading that figure. Thank you

Note that in theory, an unusually dry airmass would also cause the air column to contract so that the isobaric surfaces were closer together than normal, having the same effect on the altimeter as an unusually cold airmass, and similarly, an unusually humid airmass would have the same effect on the altimeter as an unusually warm airmass.  But I suspect the possible effect from humidity variations is much less than the possible effect from temperature variations.

Makes sense. In fairness, the figure from the OP is really confusing due to the large red arrows. I knew I understood the general concepts and that picture just flipped my entire understanding.

if I am at sea level and the temperature suddenly dropped, would I think.
I'm in the mountains?

if I am at sea level and the pressure level suddenly dropped, ... , would
I think  I'm in the mountains?

You really need to brush up on the concept of density altitude.
Instead of playing "3 card monte" with these concepts, it is recommended to take a methodical approach.
Your plane "thinks" exactly like you do regarding temperature, pressure, and density, or, better put, the engineers who wrote the POH took great care to make performance charts and graphs based on pressure altitude corrected for temperature.
It is density altitude you are after to answer your questions. Get into your POH and just plug in some numbers. For pressure altitude, set your Kollsman to 29.92, then use OAT in Celsius to determine density altitude. Density altitude is the altitude you and your plane "feel".

Density Altitude = Pressure Altitude + [120 × (OAT - ISA Temp Celsius)]

The bit about IA relative to TA pertains to when you are flying nearer to the ground and use the local ground atmospheric pressure to determine AGL. The errors introduced in your altimeter from temperature variation can become significant when it is very cold (look out below).  There are also charts available for these effects.

Pressure is proportional to density AND temperature

It might be best to get away from the "stack of air" analogy and to apply the "triangle" relationship to your altimeter, which is calibrated to ISA.

if temp is higher than ISA, than thinner air will give the same pressure.

This is why you are higher than you think you are.

if temp is lower than ISA, then denser air is needed for the same pressure.

This is why you are lower than you think you are.
So, it comes down to the altimeter, which reads pressure.  The corrections for ISA are the same, the only difference is that one uses local pressure to determine AGL, and corrects that for temperature, rather than 29.92.

More reading about ISA and lapse   rates.


text:
Is temperature inversion good or bad?
When there is temperature inversion, I heard that convection is suppressed and hence the layer of air is stable.
But I also see the following questions when studying for my PAR:

A pilot can expect a wind shear zone in a temperature inversion whenever the windspeed at 2000-4000ft above surface is at least 25 kts.

Hazardous wind shear can occur near the ground with either thunderstorms or a strong temperature inversion.

Hazardous wind shear can be expected in area of low level temperature inversion, frontal zones, and clean air turbulence.

Smooth air, poor visibility, fog, haze, or low clouds should be expected beneath a low level temperature inversion layer when the relative humidity is high.

So is inversion good or bad?
A slightly related question: Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow across a mountain ridge, and the air is unstable.
This leads me to believe that you can have turbulence while there is stable air. But I don't quite understand how. This seems contradicting to me. I'd not call air stable if there's turbulence. Can anyone shed light on this?

I would suggest breaking these into two separate questions as per the help center. The answer to each question is unrelated apart from being in the topic of meteorology

"Good" and "bad" are very subjective:  If you get airsick and hate turbulence then smooth air is good.  If you despise poorer visibility but don't mind getting bounced around then a more convective system might be to your liking.  They also vary by degrees.

"Is temperature inversion good or bad?" -- are you a glider pilot looking for good thermals, or looking for a smooth conditions for your first flight in a powered paraglider?

"A slightly related question: Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow across a mountain ridge, and the air is unstable." -- the accuracy of this statement, or lack thereof, would make a good ASE question.  Mountain waves are in fact generally associated with a STABLE airmass.

You could also ask a question about the specific meaning of the word "stable" in the context of the atmosphere.  It has to do with the temperature lapse rate-- will a given parcel of rising air tend to stay warmer and less dense than the immediately surrounding airmass, or not.  As you've noted in your question, certain kinds of turbulence are in fact associated with stable air.

To answer the first part, I wouldn't think of inversion being good or bad. It's just something that exists and a pilot should understand what it means. Inversion does have effect on weather and a/c performance, but you can't directly equate that to good or bad, it depends on the situation.
The second part, can turbulence exist in stable air? Most certainly yes it can.
Thermal turbulence, however doesn't. Thermal turbulence is the one you get when sun heats the ground and the adjacent warm air rises. This requires unstable or conditionally unstable air. However this is just one type of turbulence.
Stability of air mass would, with a fair amount of simplification, answer to a question "can thermal convection exist", but there are multiple other factors than thermal convection that cause turbulence.
Turbulence in general is a distrubed flow of air, very often caused by vertical currents disturbing the horizontal flow. In a mountain wave situation the wind sheering away from the mountain is deflected back towards the ground and stuck in a wave motion because of stability differences. This causes notable turbulence.

Other types of turbulence you might find in stable air are mechanical (frictional) turbulence caused by objects such as buildings, coastlines or treelines, turbulence caused by wind direction or velocity changes in jetstreams. There's also almost always some turbulence at the tropopause level etc.


text:
What is the correct phraseology for declaring a fuel emergency?
If I am  pilot, approaching my destination airport and realise that, after landing I will have less than 30 minutes of fuel remaining, how exactly should I express this when communicating with ATC?

in ICAO rules
in FAA rules
in EASA rules

For example, in a country where Spanish is an approved ATC language, would it be sufficient to say "ABC12345 FL210 en acercamiento y solicitamos prioridad para la aproximación. Al momento se nos ha presentado un problema de combustible" ("ABC12345 FL210 inbound and we request priority for the approach. Right now we have a fuel problem")

Have you looked up any of the FAA and EASA regs on the terms "minimum fuel" , "emergency fuel" and 'declaring an emergency?"  The FAA's AIM used to have the rules on that ...

@KorvinStarmast: That is a good point - As a non-pilot, I've had trouble locating definitive documents from ICAO. Especially in Spanish. My question was motivated by a related but off-topic question - I thought the author of that question might find answers to this (hopefully on-topic) question useful to them.

a part of your question is unclear to me: why are you asking about FAA and then go to make an example about a Spanish-speaking country? what are you trying to get?

@Federico:  I wonder if the poster has Avianca Flight 52 in mind.

@Michael: Partly. If, for example, the exact meaning and pronunciation of PAN PAN is the same everywhere, it would presumably help situational awareness when say an aircraft from an English speaking country and an aircraft from a Spanish speaking country are both in the vicinity of an airport in another Spanish speaking country and hearing aircraft/ATC communications in either language.

Is this about the crash in Colombia with the Chapecoense football team on board?

@Dediqated: No. See accident speculation

Medellin seems prone to such occurrences.  Btw, asking this general question because of an accident, even while the investigation is ongoing, is different from speculating about that accident. Clarifying proper procedures is a necessary prerequisite for anybody to form their own opinion based on accessible facts.

(This is very closely related to this question, and see this one too.)
At least in the US, cutting into fuel reserves isn't an emergency by itself. But assuming that things have gone beyond "minimum fuel" and you clearly need priority for landing then you should indeed declare an emergency.
The wording you mentioned seems 'weak' to me; if you do have to declare an emergency, there should be no possible doubt about it or about what you need. Assuming that I was already in contact with ATC, I'd probably say something like this (see the AIM 6-3-2):

Mayday, mayday, mayday. Louisville Approach, N12345 is declaring an emergency, low fuel. We are now direct runway 35R for landing. 3 on board, 15 minutes fuel remaining.

Note that if time is critical I'm not going to "request" anything, I'll just tell ATC what I'm doing and let them sort out the rest. That phraseology and statement of intentions should be understood anywhere in the world.

The last paragraph sums it all up nicely.  The fuel starvation crashes have all, to my (uncertain) knowledge, been caused because the commander do not assert themselves and tell the world "this is what is going to happen, get everyone else out of my way".

ICAO
According to an IFALPA Briefing Leaflet of 2012 "Amendment 36 to ICAO Annex 6 Part I"

The pilot-in-command shall advise ATC of a minimum fuel state by declaring MINIMUM FUEL when, having
  committed to land at a specific aerodrome, the pilot calculates that any change to the existing clearance to that aerodrome may
  result in landing with less than planned final reserve fuel.
Pilots should not expect any form of priority handling as a result of a “MINIMUM FUEL” declaration.
The pilot-in-command shall declare a situation of fuel emergency by broadcasting MAYDAY, MAYDAY, MAYDAY,
  FUEL, when the calculated usable fuel predicted to be available upon landing at the nearest aerodrome where a safe landing
  can be made is less than the planned final reserve fuel.

EASA
The EASA guidance seems to be identical to ICAO guidance.
For example, the following text has been attributed to EHAM airport briefing (Jeppesen 10-1P10)

Only when the pilot declares an emergency, radio call prefixed by MAYDAY (3x) for distress or PAN PAN (3x) for urgency, priority handling will be provided. Calls such as “low on fuel” have no status in the Amsterdam FIR.

Related (see Pondlife's answer)

Do I have to declare an emergency if I cut into fuel reserves?

When should the term "pan-pan" be used instead of "Mayday"?
How does ATC handle different kinds of emergencies?
Who has the higher authority, the pilot in command or ATC?

Interesting, and probably sensible, that they would rather have you divert than declare an emergency.

In Australia, from 8 November 2018,

... the fixed fuel reserve for day visual
flight rules (VFR) for piston or turboprop small aeroplanes
is 30 minutes.

and

When conducting these checks, you may discover that you would be landing at your original planned destination without sufficient fuel, that is, your fixed fuel reserve remaining.
If this occurs, make an alternate plan to land safely with sufficient fuel at a different location than you had originally planned. Your new safe landing location will depend on your aircraft capabilities and the conditions.
However, if a safe landing location is not an option and you are landing with less than your fixed fuel reserve [30 minutes of fuel], then you must declare Mayday Fuel.

Thus under your scenario, it would be MAYDAY MAYDAY MAYDAY FUEL ...
https://www.casa.gov.au/publications-and-resources/standard-page/fuel-requirements-australian-aircraft

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Where can I find information on dethermalizer aerodynamics?
A dethermalizer is a device that alters the aerodynamics of an airplane, glider etc, allowing it to descend quickly.
Are there any sources - including equations and derivations - on dethermalizers, as (most often) used on free flight model planes?

Source: Youtube.
The most detailed information I've found so far is NASA's low speed controlled deep stall sailplane tests, which contain many measurements graphs and verbal descriptions, but no math to explain this behavior.

NASA Technical Paper 3022, 1990
NASA Technical Memorandum 86041
NASA Technical Memorandum 85917

That's the kind of ride that will get your passenger's attention! It looks to me like the tail is designed specifically to cause a stall for testing purposes. Is that what I'm seeing?

Based on my observation of free flight models, the slab elevator is designed to stop or reduce forward motion, stalling the wing, and ideally causing the plane to descend straight down while pitch and yaw remain approximately level.

Again based on observation - as I've seen no wind tunnel test streamlines - the main difference between a dethermalizer's operation and an ordinary "deep stall", is that with the DT, the elevator is not immersed in the turbulent wake of the stalled main wing. It maintains relatively clean airflow over the tail surfaces allowing some measure of directional and "glide angle" control. The NASA glider tests were the first intentional use of a DT on any full size aircraft that I'm aware of, however the Wright Brothers did described this apparently accidental maneuver with one of their gliders.

Correction: pitch and Roll remain approximately level, with the rudder - depending on design - allowing some yaw control.


text:
What is wing inductance?
I am currently trying to understand the ground roll and climbing stage of normal aircraft.
I came across this formula which is an expression of the airplanes drag:
$X_a = c_{{x}_a} S \frac{\rho V^2}{2}$
where: $ c_{{x}_a} = c_{x0} + A c^2_{x_{a}}$

S: wing area
$\rho$: air density
V: velocity
$c_{x0}$: drag coefficient when the lifting force = 0
$c_{x}$: drag coefficient

A is said to be the wing inductance. Could somebody explain what is meant by wing inductance?

Are there typos in your formulae?  Should the second one not be $c_{x_a}=c_{x_0}+A c_{z_a}^2$ where $c_{z_a}$ is the lift coefficient?

@Christo nope, no mistakes this is the formula that I was provided. Unless there is a mistake in the docs I was given...

$$A = \frac{1}{\pi \cdot e \cdot AR}$$
where
$\pi = 3.14159....$, $e$ is the Oswald efficiency factor, and $AR$ is aspect ratio of the wing.

This answer would be better if it explained the physical significance of this number.

It would indeed be nice if you could explain the physical significance of this number.

The drag of a conventional aircraft is
$$
D = \frac{1}{2}\rho V^2 S C_D
$$
where
$\rho$ is the air density,
$V$ is the true airspeed,
$S$ is the wing reference area, and
$C_D$ is the drag coefficient.
The drag coeffcient can be approximated by
$$
C_D = C_{D_0} + \frac{C_L^2}{\pi eA\!R}
$$
where
$C_{D_0}$ is the zero-lift drag coefficient,
$C_L$ is the lift coefficient,
$\pi=3.1416\ldots$,
$e$ is the span efficiency factor (also called Oswald's efficiency factor), and
$A\!R$ is the aspect ratio of the wing.
The term
$$
\frac{C_L^2}{\pi eA\!R}
$$
is called the induced drag coefficient.
I suspect that there is a typo in the document where you obtained your formulae.
The second formula should be $c_{x_a} = c_{x_o}+Ac_{z_a}^2$ corresponding to $C_D = C_{D_0} + C_L^2/(\pi e A\!R)$.
In that case, the $A$ in your second formula corresponds to $1/(\pi e A\!R)$ as @Jared pointed out.
The term "wing inductance" that your source uses is probably some variation of the term "induced drag" due to the wing.
You can read this Wikipedia article to find out more about "induced drag", also called "lift-induced drag".


text:
Why do we need to know both groundspeed and airspeed?
As far as I understood it correctly:

airspeed: is obtained by measuring the difference in airpressure (using Pitot tubes I guess?) around the aircraft and the airpressure caused by propulsion.
ground speed: is the speed of the aircraft relative to the (immobile) ground.

Ok, I see that there are two types of speed. But why do we need both? Why not just one?

Without groundspeed, how would you  know how long it will take to get from A to B?

And why do we need True Airspeed too? :)

Because ground speed doesn't directly translate to V speeds, and V speeds don't directly translate to ground speed.

@RonBeyer That's going to mean nothing to the OP.

(Assuming no GPS, as was the case for most of aviation history) You need true airspeed to find how fast you're moving relative to the airmass, then you can use wind weather data to approximate how fast you're moving relative to the ground, to find out how far you've traveled and how long your journey will take.

That's pretty impressive - 4 answers before this was closed as a dupe!

The aircraft wing is only "aware" of the air flowing over it, and air moves relative to the ground - wind. Meaning, the airplane performs - flies - based on airspeed and we know when we'll get to our destination based on groundspeed.

Airspeed is critical for pilots, because it is what the airplane "feels" when it's flying. Too little airspeed and the wings won't generate enough lift to fly, too much and the plane can be damaged. (And you're right, the pitot tube, along with the "static port" is what allows airspeed to be measured.)
Groundspeed is how quickly you're getting where you're going. This is also important, because the engine (or engines) consumes an certain amount of fuel per hour. If you are flying between two airports that are 400 miles apart in a plane that goes 100MPH, with no wind your trip will take 4 hours. If you have a 20MPH headwind your airspeed will still be 100MPH but your groundspeed will be reduced to 80MPH, and your trip will take 5 hours instead of 4. If you've only got 4.5 hours worth of fuel, you're going to need to make a stop. It's really good to know this before you leave!
So airspeed is how fast the plane is flying through the air and groundspeed is, as you observed, how fast you're getting where you're going. Both are important!

This would be better if you pointed out that airspeed is really a proxy measurement for AoA (alpha)

@UnrecognizedFallingObject: Thanks for your comment! Two replies... 1) I don't think a discussion of AOA would have helped the questioner's understanding of airspeed vs. groundspeed. 2) AOA is independent of airspeed, so I wouldn't agree airspeed is a "proxy" for AOA. Your point, I think, is that airspeed gives us only an indirect and approximate way of knowing when critical AOA is being approached. With this I agree. Rather than calling airspeed a proxy measurement for AOA, maybe we can agree that "poor substitute" is a better term! (Though I still need airspeed to stay below Vne.)

Yeah -- I never said it was a good proxy for AoA!

Welcome to Aviation.stackexchange David Vancina. Nice first post!

A short way of saying this is airspeed is for "aviate" and groundspeed is for "navigate". I guess the third speed would be speed of light for "communicate"!

Keep in mind there are several types of airspeed.
Indicated Airspeed (IAS) is Airspeed based upon the ratio of stagnation vs static ambient air pressure where the airplane is flying.
Calibrated Airspeed (CAS) is Indicated Airspeed corrected for installation and equipment error.  It reflects a more precise airspeed at STP based upon the installation.
True Airspeed (TAS) is the indicated Airspeed corrected for nonstandard pressure and temperature.  It reflects the actual speed of the relative airflow over the aircraft.  In still air, the TAS is equal to the groundspeed.
Groundspeed is the speed the aircraft is crossing over the ground at.  It will be equal to the sum of the true airspeed of the aircraft and the headwind component of the wind aloft at the altitude the airplane is flying at.
It becomes important to differentiate and understand these terms as they will play an integral role in your time distance and fuel calculations in order to know whether you can safely complete a flight.  Flight planning does not use linear range as a metric so much as it relies on total available time aloft.  Fuel tanks carry known quantities of fuel and engines burn fuel at specific rates at specific power settings at specific altitudes resulting in specific true air speeds during the climb, cruise and descent portions of the flight.  Divide the total fuel on board by the rate of fuel consumption, and you know your total flight time available.  You will then need to know the winds aloft information to calculate your forecasted groundspeed in order to know if you can safely complete the flight.
Fail to perform these calculations correctly, and you could face a forced landing or a ditching from fuel starvation.  If upper level winds are stronger than forecast on a fuel critical flight i.e. one that's planned to be very close on fuel aboard, you will need to be able to make these calculations en route to know whether you will need to divert to an alternate airport or you can press on to the planned destination.  This happens a lot both with small aircraft as with this SR-22 which ran out of fuel due to strong headwinds while on a ferry flight to Hawaii and even in large jets.  Bangor International in Maine is a alternate for aircraft crossing the Atlantic who get into trouble as is Hawaii and Samoa for Pacific Rim routes.

KIAS (knots indicated airspeed) is the speed which is indicated in the cockpit. It's the aircraft's relative speed through the surrounding air. This speed is crucial for the flying performance of an aircraft because it's the speed which is used to describe the minimum speed and similar important airspeeds.
GS (groundspeed) describes the aircraft's speed relative to the ground. So if an airplane has a groundspeed of 100kts it will fly 100nm per hour relative to the ground. This speed is influenced by the head- and tailwind; the GS will be higher than the IAS if the aircraft experienced tailwind and vice versa.
To calculate time needed to fly a fixed distance you need the GS, as indicated airspeed also describes the speed of the air moving towards you (that means if you are standing on the ground experiencing 40kts headwind, the speed indicator indicates 40kts (as it's calibrated to IAS)).

Indicated airspeed is, actually, not a speed at all. It is a measure of dynamic pressure. At higher altitude, indicated airspeed is less than true airspeed.


text:
Why do we calculate the pitching moment coefficient about quarter chord point?
Why do we calculate the pitching moment coefficient about quarter chord point, when force and moment system can be transferred to any convenient point?

There might be some helpful info at http://aviation.stackexchange.com/q/31878/8730

Because the quarter chord point is the most meaningful point: the wing or surface lift vector can be found here. Like taking the CoG as reference point for gravity forces.
Theoretical and practical analysis have shown that if the moment and force reference point is taken at 25% of Mean Aerodynamic Cord (MAC), the magnitude of the aerodynamic moment remains nearly constant when the angle of attack changes. This location is called the wing's Aerodynamic Centre (AC).
The lift and moment system can be transferred to any convenient point, but that is the point of the quarter chord point :)

The aerodynamic center is the point at which the pitching moment
  coefficient for the airfoil does not vary with lift coefficient (i.e.
  angle of attack), so this choice makes analysis simpler

Wikipedia
And, the aerodynamic center is found approximately at quarter chord length from the front.


text:
Why can't this blended wing body trijet airliner fly?
I was told in this other question this aircraft was not real, and that it could not fly in this design.

I'm now interested in knowing what would prevent it to fly, from an engineering point of view. It looks great... why is it so obvious this cannot work?

What makes you say that it would not work?

@egid as I commented on the other post, main gear too forward, for example?

My take is that the CG is far forward, and the center of lift is behind the main gear.

Because (as I look at the picture closely) it appears that the outboard section of the left wing is in the process of breaking off?

Passenger evacuation for one. Right now, you can open some doors on the side of the tube and add more doors if needs be. That's a lot more of a challenge here.
Also, distributing passengers to a wider area inside the body can lead to greater instances of motion sickness.
Passengers will generally prefer having windows, which is also a challenge for this type of aircraft.
Main gear should be far enough forward that most of the weight is on it, but far enough aft that the nose isn't unloaded in aft CG conditions. It might be right where it needs to be. You'd have to know the CG location. You also need to account for an empty airplane with minimal fuel or it could tip up onto the tail. Tip up.
A large lifting area should at least mean slower landings, but gear should be long enough or far enough aft to flare a bit. You want the mains to touch first so you don't bounce or damage the nose gear.
It's not so much that it can't be done, but there are challenges.

Re "Passengers will generally prefer having windows...", I'm not sure about that.  The few times I've flown commercial, it seemed that most of the other passengers were far more interested in watching the in-flight TV.

Well, you do know the CG location. Or more precisely: the CG must be just before the quarter (average) chord and it must be a just little more before the main gear. Therefore the main gear must be just after the quarter-chord. But it's well before it!

That picture appears to be a photoshop assembly of real aircraft bits from common landing/take-off shots, made to fit the shape of a NASA X48, an unmanned flying test aircraft about the size of an ultralight. Whoever did the photoshop job even slavishly copied the undercarriage position (but not the relative undercart length/height) of an extremely lightly built, largely empty, model aircraft.
It certainly can fly.
https://www.nasa.gov/topics/aeronautics/features/bwb_main.html

I believe the challenges to using BWB as a people mover are the motion sickness and evacuation issues. Soluble, but challenges nonetheless. Of course, airport and runway suitability are possible issues as well. Military airlift is a probable first application for BWB.

What's BWB? Inline more information will help aircraft enthusiasts that might not know much :)

Blended Wing Body.


text:
How is the airfoil of a fixed wing ultralight constructed?
This is a good example of the type of ultralight I am trying to build:

(Source)
How might the airfoil be constructed in this plane?
My guess was that it's mostly created by the cables that suspend it, but then again, one like this:

(Source)
Doesn't have those cables, so how are the wings constructed?

wood?
a bag of helium?
something else?

If you could link me to some sort of visual it'd also be much appreciated.

There are various ways to build a wing like this. Ultimately you need something to shape the rigid form which you then pull fabric over. The cables do not provide the wing shape they provide support for the length of the wing. This goes back to the fairly early days of aircraft design for heavier than air flight,

In 1909,Frenchman Louis Bleriot produced an aircraft with notable design
  differences. He built a successful mono-wing aircraft. The wings were
  still supported by wires, but a mast extending above the fuselage
  enabled the wings to be supported from above, as well as underneath.

Mast/cable wings fell out of popularity as spar supported wings became viable in the early days of heavier than air flight.

As early as 1910, German Hugo Junkers was able to build an aircraft
  with metal truss construction and metal skin due to the availability
  of stronger powerplants to thrust the plane forward and into the sky.
  The use of metal instead of wood for the primary structure eliminated
  the need for external wing braces and wires

You can use wood like this. Or wood with a foam core.

(source)
You can also achieve the same goal with a metal rib assembly.

(source)
If you have the budget carbon fiber is also an option.
There are a few ways to cover the wing frame once its complete but ultimately the fabric must be pulled over the form and, in some capacity, shrunk to make it taught.
Fabric covered wings have lead to some of the most successful airplanes in history. There is quite a bit of info out there on how to work with fabric in relation to aircraft. The FAA has a nice handbook on it here and more info here.
If you intend on building something I would take a look at this site about building a Breezy. It looks like you can even get a full kit for one here.

Thanks for the detailed response and I apologize for taking a week to respond. My follow-up question for this would be (since ultralights in the US are defined as being less than 254lbs and seat only 1) is wood a viable option for making a plane this light? I have to create an entire chassis and hold an engine and a propeller so that's why I was worried about the weight of wood getting in the way. The breezy is a two seater, so I can't follow it exactly, but otherwise its design is what I'm going for. Since you didn't say anything about the helium bag option, I assume it's not viable?

@TrapAlcubierreDrive I dont know much about the helium bag style design so I refrained from commenting. You could always go for a single seat breezy. Balsa wood is not terribly heavy and if weight is a concern, carbon fiber is an option. There are lots of designs and kits out there for this you may want to start off with a kit to get an idea of how these things are built.

Yep I found a good PDF showing the construction of an ultralight on this page. (link: https://grabcad.com/library/ultralight-airplane) It's the PDF labeled Fighter. Regarding balsa wood, I've see it used in model airplanes, but for the most part I thought it was pretty weak and so I'm wondering how well it would stand up to being on an ultralight. Is there any variety of it that you might recommend or that is used often in airplanes? I don't have the money for full carbon fiber construction, though I may make the spars out of it, since they don't use as much material as airfoil pieces.


text:
What does "CC (Charlie Charlie)" mean when pilots reply to ATC?
I heard a pilot replied "CC" to ATC instruction.
I can't remember the exact situation, but does anyone knows what it means?

Can you clarify did you hear "CC" or "Charlie Charlie"

Short answer
Charlie-Charlie is a fancy substitution for a standard affirmative.
It comes from the convention of abbreviating Correct/Yes by letter C in codes. It was early standardized and used at sea since 1857. Under the Commercial Code of Signals (1857-1902), the C flag, in addition of representing the letter itself, had the meaning of Yes/Affirmative.

C flag meaning affirmative
This code has been improved and extended into the International Code of Signals (ICS). While the visual representation changed, the meaning was preserved extended to radiocommunications. From the 2003 ICS:

Signals for flags, radiotelephony, and radiotelegraphy transmissions.
C: Affirmative—YES or “The significance of the previous group should
be read in the affirmative”.

Examples
Discovered by @ymb1, this accident investigation report, for a Boeing 747 accident in 1987, includes a transcription of the pilot (CA) controller (MA) exchange:

CA: Roger, we will appreciate it if you can alert, er,
fire, er, er, er.
MA: Do you request a full emergency please? A full emergency?
CA: Affirmative, that's Charlie Charlie
MA: Roger, I declare a full emergency.

later:

MA: Confirm runway one four?
CA: Charlie Charlie.

And this other document, still from @ymb1:

Do you have ATIS information Delta?
Charlie Charlie we have Delta.

...

Ok our stand 41 AF028.
Understand B 41.
Charlie, charlie.

Formally, "roger," "wilco," and "affirm/affirmative" are not synonyms.  "Roger" means "I understand," "wilco" means "I will comply," and "affirmative" means "yes."  Usage does differ from the formal meaning, however.

Is this some kind of elaborately layered pun? Charlie -> C -> "C" is pronounced Si (spanish for yes) -> yes

@BlackThorn: Yes, mnemonic, also No-vember. I'm a little unsure whether "I require medical assistance" being Whisky is a joke or based on reality :-)

@WayneConrad: does "affirmative" mean "I understand", "I will comply" or what?

@smci "Affirmative" is "yes" in response to a yes/no question. "Negative" is "no".

From the ICS ......CC I am (or vessel indicated is) in distress in lat… long… (or bearing… from place indicated, distance…)
and require immediate assistance (Complements Table 2, Chapter 2, Section 10, Page
104 if required)    How does this apply  to ATC?

@RoyC: The flag "C" means "Yes", and Charlie is equivalent to "flag C" in the mouth of the pilots who use this non standard terminology.

Sorry you are referencing the ICS which has multi letter meanings and then
you are telling us that that is not really what is being used and the pilot is saying Affirmative Affirmative?

@RoyC: Affirmative. But if you want to chat, then let's go to the chat.

FWIW, there are some competing theories on what CC really means, including this naval one. No one seems able to quote a source.

@RoyC: "From the ICS ......CC I am (or vessel indicated is) in distress in lat… long (...) Section 10, Page 104". You are looking at the Morse code part of the ICS.

It could also be a the short for the aircraft registration.
Twr: G-CD, report at point Papa
G-ABCD: Charlie Delta
I have no idea how formally correct it is but when using shortened registration for calls (obv it has to be initiated by the twr) and the info is not critical it is often heard.

CC is short for Click Click. In situations where a military operator was busy or where talking could prove fatal an incoming message would be acknowledged by a double click of the transmit switch on the radio producing a "click click" at the other end.
"CC" somehow got into informal usage rather than the more precise roger wilco or affirmative. In this context it would probably be used as an informal acknowledgement of a purely informational message.

Second that, I remember being taught this method of "silent affirmation of receipt" in the US Marines FROC (field radio operators course).

The OP's question was about CC not Charlie Charlie.

@mins Added quotes to clarify.

To answer the OP's question, "CC" and/or "Charlie Charlie" mean absolutely nothing in air traffic control. In my 30+ years in ATC, I never heard, nor heard of, someone responding to a clearance with that verbiage. If I did, I would repeat the clearance because I had not received a valid read back.

Flying overseas in the 1970s we used "Charlie Charlie" (not CC) as affirmative mostly on HF (High Frequency) radios.  UHF, VHF and FM radios were pretty clear and you could understand a word like affirmative.
But HF was often a weak signal; scratchy and full of static.  Charlie Charlie (repeated like that) was better- easier to understand- than one word answers like affirmative.  I was a young pilot then and I learned to use it from professional radio operators.
I will defer to the other responder regarding it's historical origin.

Welcome to Aviation.StackExchange!

"Charlie Charlie" was always "Confirmed Correct" in my understanding.
If ATC asked a question like "Is that your final requested level" then "Charlie Charlie" was an acceptable and recognised informal reply.


text:
What is the history of "Joker" and "Bingo" fuel terms?
Why do we use, in military aircraft, the words "Joker" and "Bingo" to indicate the fuel status of the aircraft? What is the history of these two terms?

Bingo is used because it is phonetically easy to be distinguished, like using niner instead of nine because the latter sounds too much like nein in German ("no"). Joker is used because the additional fuel is a wildcard option to get to one or more alternate landing sites.

"Bingo" originated with aircraft carrier operations.  "Bingo" actually means to divert.
The official US Navy definition of "BINGO" is: "An order to proceed and land at the field specified, utilizing a bingo profile. Aircraft is considered
to be in an emergency/fuel critical situation. Bearing, distance, and destination shall be provided."
CV
NATOPS MANUAL

If the aircraft carrier was operating in an area that had a land based alternate airport, it would be called "Bingo Ops". "Bingo Fuel" was the amount of fuel remaining to safely reach the "Bingo Field". The "Bingo Field" was the closest land based airfield which could be used as a backup in case the aircraft was unable to land on the aircraft carrier for any reason. Examples could be a fouled deck due to a disabled aircraft, or unusable arresting gear system.
Other military, and even civilian operators, have since adopted "Bingo Fuel" to mean minimum fuel to safely reach an airport.
My own research shows that there is no definite answer to the origin of Bingo.
"Joker Fuel" is a predetermined amount of fuel in excess of Bingo Fuel.

bingo fuel was fuel gauge malfunction estimated time of flight to rely on but I would rather play it safe
joker fuel was "wild card" your guess is as good as mine however I bet you my guess is better than yours, initiating to command and everyone else listening in that, you have doubts about ground support and that you think the enemy could be amongst you.

Welcome to aviation.SE. You should read the help center and highlight what your answer adds to existing ones.

Carl, you can edit your answer to correct any typos, I'll correct the one you mentioned in a comment (posted as second answer).


text:
Can I get a FAA medical certificate and apply in an Indian airline?
I am an Indian, and was wondering if I could get an FAA medical certificate and apply in an Indian based airline.
Is there a problem if I do that? Should I get the DGCA medical certificate itself?

According to my knowledge, To be employed by an Indian airliner you have to get a DGCA medical Certificate.

Can you expand on this answer with quotes of any relevant regulatory language establishing this claim?

Well Air India is hiring qualified pilots here. The advertisement says you need a medical certificate issued by the DGCA. There is no mention of accepting an FAA certificate.
I'm not completely sure how it works in India but usually you need to get a medical certificate from the country in which the airline is based (or to be specific, the country in which the aircraft is registered). I'm not aware of any exceptions to this rule except for temporary operations, but I stand to be corrected.


text:
How many layers do the Boeing 787 cabin windows have and what might make them fail?
I am interested to know how the Boeing 787 cabin windows are made. Specifically, how many layers do they have and what can make them crack in-flight?

This article about the Boeing 787 Dreamliner states that

[...] The Dreamliner’s new windows are made of two thin layers of glass with gel wedged between them. [...]

The windows have also a failsafe mechanism in order for the outer pane to crack or fail first, it's this tiny hole that you may have noticed, which serves to regulate the pressure exerted from the cabin to the window.
I couldn't find a more technical article about aircraft windows, but I found an AIAA article about Space Shuttle's cockpit window system, if you are interested about something a little bit more extreme!